Technical Report No. 6-92
Radiation-related small head sizes among prenatally exposed atomic bomb survivors
Otake M, Schull WJEditor’s note: A publication based on this report was published in Int J Radiat Biol 63(2):255-70, 1993.
Summary
The population prenatally exposed to the atomic bombings of Hiroshima and Nagasaki, referred to as the In Utero Clinical Sample, on whom Dosimetry System 1986 doses are available consists of 1566 individuals (1242 in Hiroshima and 324 in Nagasaki). Of these study subjects, 1473 had the circumference of their heads measured at least once between ages 9 to 19. Among these 1473 individuals, 62 had small heads–the circumference of the head was two standard deviations or more below the observed specific age-at-measurement mean. Twenty-six of the 30 cases with severe mental retardation described elsewhere are included among these subjects. Of these 26 severely mentally retarded cases, 15 (58%) had small heads. Most (86%) of the individuals with small heads were exposed in the first or second trimester of pregnancy–55% in the former period and 31% in the latter.
Various dose-response relationships, with and without a threshold, have been fitted to the data grouped by the trimester or postovulatory age (weeks after ovulation) at which exposure occurred. A significant effect of radiation on the frequency of individuals with atypically small heads is observed only in the first and second trimesters and for the intervals postovulation of 0-7 weeks and 8-15 weeks. Although the risk of a small head at 0-7 weeks postovulation increases significantly with increasing dose, no increase in risk for severe mental retardation is noted in this period. No excess risk of a small head was seen in the third trimester or among individuals exposed at greater than or equal to 16 weeks postovulation.
The estimated threshold, based either on a linear or a linear-quadratic dose-response relationship, is zero or thereabouts. This apparent absence of a threshold and the somewhat different periods of vulnerability suggest an embryological difference in the development of both a small head and mental retardation. Mean IQ (using the Koga test) and its standard deviation are 63.8 and 8.5, respectively, for the severely mentally retarded cases with small heads and 68.9 and 11.9 for the severely mentally retarded cases without small heads. These values are 96.4 and 19.8 for cases with small heads only. The mean IQ and standard deviation for the overall sample are 107.8 and 16.4, respectively. No significant difference exists between the first two IQ means identified above, but both are significantly less than the mean for individuals with small heads but without severe mental retardation. The mean IQ of individuals with small heads but without severe mental retardation does not differ significantly from the mean for the entire sample. The relationship of small head size to four other anthropometric measurements (standing height, body weight, sitting height, and chest circumference) is described.
The population prenatally exposed to the atomic bombings of Hiroshima and Nagasaki, referred to as the In Utero Clinical Sample, on whom Dosimetry System 1986 doses are available consists of 1566 individuals (1242 in Hiroshima and 324 in Nagasaki). Of these study subjects, 1473 had the circumference of their heads measured at least once between ages 9 to 19. Among these 1473 individuals, 62 had small heads–the circumference of the head was two standard deviations or more below the observed specific age-at-measurement mean. Twenty-six of the 30 cases with severe mental retardation described elsewhere are included among these subjects. Of these 26 severely mentally retarded cases, 15 (58%) had small heads. Most (86%) of the individuals with small heads were exposed in the first or second trimester of pregnancy–55% in the former period and 31% in the latter.
Various dose-response relationships, with and without a threshold, have been fitted to the data grouped by the trimester or postovulatory age (weeks after ovulation) at which exposure occurred. A significant effect of radiation on the frequency of individuals with atypically small heads is observed only in the first and second trimesters and for the intervals postovulation of 0-7 weeks and 8-15 weeks. Although the risk of a small head at 0-7 weeks postovulation increases significantly with increasing dose, no increase in risk for severe mental retardation is noted in this period. No excess risk of a small head was seen in the third trimester or among individuals exposed at greater than or equal to 16 weeks postovulation.
The estimated threshold, based either on a linear or a linear-quadratic dose-response relationship, is zero or thereabouts. This apparent absence of a threshold and the somewhat different periods of vulnerability suggest an embryological difference in the development of both a small head and mental retardation. Mean IQ (using the Koga test) and its standard deviation are 63.8 and 8.5, respectively, for the severely mentally retarded cases with small heads and 68.9 and 11.9 for the severely mentally retarded cases without small heads. These values are 96.4 and 19.8 for cases with small heads only. The mean IQ and standard deviation for the overall sample are 107.8 and 16.4, respectively. No significant difference exists between the first two IQ means identified above, but both are significantly less than the mean for individuals with small heads but without severe mental retardation. The mean IQ of individuals with small heads but without severe mental retardation does not differ significantly from the mean for the entire sample. The relationship of small head size to four other anthropometric measurements (standing height, body weight, sitting height, and chest circumference) is described.